The present invention relates to a suspension clamp for aerial electric conductors.
Conductor galloping is a phenomenon observed in aerial transmission lines when high winds are blowing across the conductors. The conductors oscillate at a low frequency, typically 0.5 to 1 Hz, and may reach peak to peak amplitudes of 10 feet or more. Conductor galloping can damage transmission towers and take down power transmission lines.
Conventional suspension clamps and spacer dampers clamp onto the conductor and suspend it from tower crossarms in such a manner that both longitudinal movement and rotation of the conductor is restricted.
It is believed that conductor galloping may be reduced or eliminated if the suspension clamp would allow rotational movement while still preventing longitudinal movement of the conductor. Therefore, there is a need in the art for a suspension clamp which permits rotation of the conductor within the clamp while restricting longitudinal movement.
In Canadian Patent No. 1,161,913 (U.S. Pat. No. 4,381,422) a spacer-damper is disclosed which includes a vice enclosing a roller bearing or sleeve bearing within which the conductor wire rests. In this apparatus, the conductor wire is not firmly fixed within the spacer-damper and a strong longitudinal force may cause the conductor wire to slip within the device. It is necessary to introduce a durable grease into the cavity containing the roller bearing and to provide a gasket seal to protect against the penetration of dust, water or the like. If any portion of the roller bearing or sleeve enclosing the wire is made of a ferromagnetic material such as steel, two additional disadvantages result. First, current in the conducting wire will produce considerable heat in the roller bearing races which may cause its premature failure. Second, the ingress of water may cause corrosion of the aluminum conductor wire as a result of its contact with the steel bearing race.
A similar spacer-damper is disclosed in U.K. Patent No. 1,320,893. In this patent, the conductor wire is clamped within a roller bearing by a resilient rubber member. This spacer also permits rotation of the conductor wire while resisting longitudinal movement. Again, a strong longitudinal force will likely displace the conductor wire within the spacer because of the tenuous hold the spacer has on the conductor wire through the resilient rubber member. Also, the bearings may overheat and fail as a result of current being conducted through the conductor wire and the ingress of dust particles.
It is also a concern with this prior art using roller bearings that the bearing races must be constructed in split halves in order to be placed around the wire, which adds complexity and expense to the device.
Therefore, there is a need in the art for a suspension clamp which mitigates the problems in the prior art.
The present invention is directed to a suspension clamp for aerial power transmission conductors. In one aspect of the invention, the invention comprises a clamp for suspending an aerial conductor, said clamp comprising:
(a) a clamshell housing which, when closed, defines an elongate central cavity and which defines two end openings on either side of the central cavity wherein said end openings have a smaller diameter than the central cavity and wherein the conductor may pass through both openings and the central cavity;
(b) two split sleeves each of which fit within the central cavity and each of which has an inside diameter slightly greater than or closely matching the outside diameter of the conductor wherein said split sleeves abut the ends of the central cavity when installed on the conductor; and
(c) a restraining sleeve which, when affixed to the conductor, fits within the central cavity, between the split sleeves and which has an outside diameter greater than the inside diameter of the split sleeve assemblies and less than the inside diameter of the central cavity;
(d) wherein the conductor may be placed within the central cavity housing such that the restraining sleeve is disposed between and restrained by the two split sleeve assemblies and the conductor passes through the said split sleeves and the end openings.
The split sleeve assemblies preferably comprise a low-friction material such as polytetrafluoroethylene. The retaining sleeve may be a compression repair sleeve which is attached to the conductor by implosion or by hydraulic press.
In another aspect of the invention, the invention comprises a deadend clamp for suspending an aerial conductor comprising:
(a) a deadend housing defining a central bore and having an internal shoulder defining an opening; and
(b) a terminal connector having an enlarged end which fits within the deadend housing and rests against the shoulder and an elongate end which passes through the opening;
(c) wherein the enlarged end of the terminal connector bears against and is retained by the shoulder but may still rotate within the housing and wherein the elongate end of the terminal connector may be attached to a terminal end of the aerial conductor.
The deadend clamp may preferably further comprise a thrust bearing disposed between the enlarged end of the terminal connector. Preferably, the deadend housing defines a cylindrical central bore and the enlarged end of the terminal connector is a substantially flat disk.